Temperature regulating clothing is useful and often necessary for people who work, live, or recreate in or near high temperatures. In addition to the extreme example of firefighting, many other types of occupations require clothing that protects workers from elevated temperatures. While these workers typically are not required to work near active fires, they may be exposed to naturally elevated temperatures, such as in hot desert or tropical climates, or exposed to temperatures that are elevated due to the proximity of heated equipment (e.g., boilers, kilns, forges, welders) and/or materials (e.g., molten steel, hot asphalt). Even extreme generation of body heat may necessitate the use of temperature regulating clothing, especially when clothing that traps in the body's heat is worn (e.g., non-permeable protection suits, welding aprons).
A number of technologies are used in clothing to regulate temperature. For example, some clothing for firefighters has reflective components that reflect heat from flames away from the body. Firefighter clothing may include insulative components that insulate the body from high ambient temperatures. Active technologies, such as pump-driven water cooling, are also occasionally used in protective clothing. However, these technologies are inadequate and/or impractical to protect a typical mobile worker or sports participant from oppressive heat.
In recent years, clothing manufacturers have incorporated passive cooling technologies into clothing such as vests, shirts, jackets, trousers, gloves, shoes, etc. For example, some clothing incorporates bladders of liquid that can be frozen solid before wear. During wear, cooling is provided by the melting of the solid to liquid. A drawback of such technology is the requirement that the clothing be frozen before each use. In addition, the use of bladders increases the chance of fluid leakage, such as due to failure of the bladder materials.
As such, manufacturers have occasionally attempted to utilize a phase change material that is able to release and absorb heat during its transition between solid and liquid phases. Phase change materials are useful for temperature regulation because of the comparatively small temperature change during phase transition. Generally, most utilized phase change materials perform a solid-to-liquid phase change when the temperature reaches the phase change materials' melting point or phase change point. Accordingly, a micro- or macro-encapsulation is typically used to prevent flow and leakage when solid-to-liquid phase change materials are used in temperature regulating clothing. For example, in US 2011/0056622 A1, a phase change material derived from natural sources (e.g., plant oils) is encapsulated with a bladder formed from a polymer membrane. However, such cumbersome macro-encapsulations, such as bladders and packages, hinder the movement of users and increase the risk of leakage.
The integration of polymers with a phase change material has permitted the pelletization of phase change materials, see, e.g., U.S. Pat. No. 4,587,279, U.S. Pat. No. 5,765,389, and U.S. Pat. No. 6,047,106, in which polyethylene glycol (PEG) is blended with a polymer to form pellets useful in energy storage or deicing. However, such technology has not proven to be safe for use in temperature regulating clothing applications that are able to efficiently control the microclimate of a human body under a comfortable temperature. Accordingly, there remains a need for improved materials that can safely, practically, and efficiently control the microclimate of a human body in temperature regulating clothing.